The subjects of this invention are a tool for holding a blade and application of this tool to friction welding of blades.
Some machine rotors include what are called monobloc bladed disks, i.e. rotor portions to which rotating blade stages are united rigidly by welding, unlike the traditional design, in which blade stands with bulb or swallow-tail shapes, or another shape of the same type, are slid into disk grooves of a complementary section. Monobloc disks are generally lighter, and this is the reason why they are preferred.
Disks proper are generally manufactured with blade sleeves, and the blades are formed separately and welded on the sleeves by a process which is normally friction welding. Finally, excess thicknesses of the blades are removed by machining. A weak point of this manufacturing process is that the blades must be held firmly during the welding, which may be problematic if they have a complex shape, notably a twisted one. In French patent 2 716 397 which covers friction welding of blades, the blades are retained between clamping jaws which press on approximately their entire perimeter near the edge for connection to the blade sleeves. This solution is practicable but does not necessarily allow the blade to be positioned with great accuracy in the machine nor at an invariable position. In addition, machining of clamping jaws with a complex supporting face may be difficult to achieve with satisfactory accuracy.
An improved tool for holding a blade is proposed as the invention. To summarise, it comprises: a frame fitted with three blade lateral supporting faces, of which a first upper supporting face is close to the top of the blade, and two lower supporting faces are close to lower portions of the blade""s trailing and leading edges; a mobile blade lock on the frame opposite the upper supporting face; two mobile clamping jaws on the frame directed towards the lower portions of leading and trailing edges in approximately concurrent but not aligned directions, and also directed approximately towards the lower supporting faces; a clamping jaw control system; and two vertical blade supporting faces.
Precise positioning of the blade is guaranteed by the support on the five faces; the clamping jaws grip the blade positioned firmly on the frame, whilst holding it on the lower lateral supports; finally, the lock is used to hold the blade pressing on the upper supporting face.
The clamping jaws are advantageously in the shape of corners penetrating into recesses of the blade made beforehand. Similarly, it is advantageous if the vertical supporting faces are formed by upper faces of the clamping jaws, faces which are horizontal, while the lower faces of the clamping jaws are inclined to make the corner used for tightening.
The control system may include transmission lifters pushing on rear faces of the clamping jaws; in the preferred forms of the invention, it is planned that these transmission lifters should include mechanisms for pushing back the clamping jaws to stop tightening of the blade when the lifters are removed, allowing the tool to be released.
This tool is easily compatible with a single control system which may include, after a control organ advantageously constituted by a screw and nut transmission system, an activation lifter acting on both the transmission lifters mentioned above.